Hitherto, sealing means 6 is disposed between an inner link plate 2 and an outer link plate 3 so as to surround a bushing 5 in a seal chain 1′ as shown in FIG. 8 for example. Lubricant such as grease is sealed in a bearing section A composed of the bushing 5 and the pin 7 by the sealing means to keep flexibility of the chain smooth for a long period of time on the basis of relative rotation of the bushing 5 and the pin 7. Because dust caused by bulk materials such as grains, coals, iron ores, lime and salt readily invade into the bearing section A in the unloading seal chain 1′ such as a bucket conveyor for conveying such bulk materials, there has been proposed to provide two rows of sealing members 6A and 6B having O-rings 12 and 13 that contact the inner and outer link plate 2 and 3, respectively, and metallic holding plates 15 and 16 for holding the O-rings (see JP Patent Application Laid-open No. 2002-160818).
As shown in FIG. 8, the seal chain 1′ is provided with a greaser 11 having an oil orifice 9 of a predetermined length perforated through the center of the pin 7 in a longitudinal direction from one end face of the pin 7, a grease nipple 10 attached at an opening of the hole and communication holes 9a (the oil orifice 9 and the communication holes 9a will be referred to as greasing holes or greasing paths hereinafter) formed toward the bearing section A from the grease orifice. Then, the greaser 11 supplies grease or the like to the bearing section A through the relatively long greasing holes 9 and 9a from the grease nipple 10 at one end face of the pin 7. Furthermore, in order to prevent the O-rings 12 and 13 of the sealing member from bursting by greasing pressure in supplying grease, the ringed holding member 15 or 16 of the sealing member is provided with an oil groove (or gap) formed into a shape of concave groove or the like for releasing the pressure (not shown).
In replenishing grease or the like by the greaser 11, there has been a case when the grease or the like solidifies on the way of the greasing path, thus clogging the greasing paths 9 and 9a and disabling the supply of the grease, because the greasing paths 9 and 9a are long in the prior art seal chain 1′. This phenomenon is apt to occur in a large conveyor chain whose greasing path is long and which is not greased so often and therefore the grease stays at the bearing section and is apt to solidify due to chemical changes such as deterioration.
Furthermore, because the prior art seal chain 1′ has the oil groove or the gap for releasing the greasing pressure, it is unable to completely seal the bearing section A by the sealing means. Therefore, the lubricant always leaks from the bearing section A, requiring operations of replenishing the lubricant by the greaser 11 relatively soon and of cumbersome maintenance. Furthermore, there is a case of bursting the sealing means because the large pressure is apt to act on the basis of the long greasing paths in replenishing the grease or the like from the greaser 11, and the oil groove or the like described above is unable to release the large pressure that acts suddenly.
Still more, because the greasing holes 9 and 9a are formed within the pin 7 on which large bending and shearing stresses act during when the seal chain 1′ is in operation, there is a risk of damaging the pin 7 due to concentration of stresses. In order to avoid such risk, pins having a large diameter are used in designing the seal chain. Along that, however, the seal chain requires bushings and rollers having a large diameter and due to that, also requires link plates having a large thickness or width, hindering lightening and cost-down of the chains.